///////////////////////////////////////////////////////////////////////////
//                   __                _      _   ________               //
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//                           /____/                                      //
//                                                                       //
//               The Next Generation Logic Library                       //
//                                                                       //
///////////////////////////////////////////////////////////////////////////
//                                                                       //
//  Copyright 2015-20xx Christoph Zengler                                //
//                                                                       //
//  Licensed under the Apache License, Version 2.0 (the "License");      //
//  you may not use this file except in compliance with the License.     //
//  You may obtain a copy of the License at                              //
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//  http://www.apache.org/licenses/LICENSE-2.0                           //
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//  Unless required by applicable law or agreed to in writing, software  //
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//  implied.  See the License for the specific language governing        //
//  permissions and limitations under the License.                       //
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///////////////////////////////////////////////////////////////////////////

package org.logicng.explanations.unsatcores.algorithms;

import org.logicng.datastructures.Tristate;
import org.logicng.explanations.unsatcores.MUSConfig;
import org.logicng.explanations.unsatcores.UNSATCore;
import org.logicng.formulas.FormulaFactory;
import org.logicng.propositions.Proposition;
import org.logicng.solvers.MiniSat;
import org.logicng.solvers.SolverState;

import java.util.ArrayList;
import java.util.List;

/**
 * A naive deletion-based MUS algorithm.
 * @version 1.3
 * @since 1.1
 */
public final class DeletionBasedMUS extends MUSAlgorithm {

  @Override
  public <T extends Proposition> UNSATCore<T> computeMUS(List<T> propositions, final FormulaFactory f, final MUSConfig config) {
    final List<T> mus = new ArrayList<>(propositions.size());
    final List<SolverState> solverStates = new ArrayList<>(propositions.size());
    final MiniSat solver = MiniSat.miniSat(f);
    for (final Proposition proposition : propositions) {
      solverStates.add(solver.saveState());
      solver.add(proposition);
    }
    if (solver.sat() != Tristate.FALSE)
      throw new IllegalArgumentException("Cannot compute a MUS for a satisfiable formula set.");
    for (int i = solverStates.size() - 1; i >= 0; i--) {
      solver.loadState(solverStates.get(i));
      for (final Proposition prop : mus)
        solver.add(prop);
      if (solver.sat() == Tristate.TRUE)
        mus.add(propositions.get(i));
    }
    return new UNSATCore<>(mus, true);
  }
}
